Common Stock Common Stock [Member] Entity Tax Identification Number Entity Tax Identification Number Entity File Number Entity File Number Legal Entity [Axis] Legal Entity [Axis] Cover [Abstract] Cover [Abstract] Title of 12(b) Security Title of 12(b) Security Local Phone Number Local Phone Number Class of Stock [Domain] Class of Stock [Domain] Soliciting Material Soliciting Material Entity Address, Address Line One Entity Address, Address Line One Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Entity Address, State or Province Entity Address, State or Province Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Written Communications Written Communications Trading Symbol Trading Symbol City Area Code City Area Code Document Information [Table] Document Information [Table] Document Period End Date Document Period End Date Junior Subordinated Debt Junior Subordinated Debt [Member] Pre-commencement Issuer Tender Offer Pre-commencement Issuer Tender Offer Entity Address, City or Town Entity Address, City or Town Amendment Flag Amendment Flag SOUTHWESTERN PUBLIC SERVICE CO [Member] SOUTHWESTERN PUBLIC SERVICE CO [Member] SOUTHWESTERN PUBLIC SERVICE CO [Member] Entity [Domain] Entity [Domain] Security Exchange Name Security Exchange Name Document Information [Line Items] Document Information [Line Items] Document Type Document Type Class of Stock [Axis] Class of Stock [Axis] Pre-commencement Tender Offer Pre-commencement Tender Offer Entity Central Index Key Entity Central Index Key Entity Emerging Growth Company Entity Emerging Growth Company